Disk-Based Gain and Phase Margins

Stability margins of feedback loops using disk-based analysis

Disk margins quantify the stability of a closed-loop system against
gain or phase variations in the open-loop response. In disk-based margin
calculations, the software models such variations as disk-shaped
multiplicative uncertainty on the open-loop transfer function. The
disk margin measures how much uncertainty the
loop can tolerate before going unstable. That uncertainty amount
corresponds to minimum gain and phase margins. These disk-based margins
take into account all frequencies and loop interactions. Therefore,
disk-based margin analysis provides a stronger guarantee of stability
than the classical gain and phase margins.

Robust Control
Toolbox™ provides tools to:

Analyze system stability against gain and phase
variations. Use diskmargin to compute the disk-based gain
and phase margins of SISO and MIMO feedback loops.

Model gain and phase uncertainty. Use the umargin control design block to analyze the
effect of gain and uncertainty on system performance and
stability.

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